1. Field of the Invention
This invention relates generally to developer mix monitors for electrostatographic machines, and more particularly to automatic monitors for replaceable development stations.
2. Description of the Prior Art
Electrostatographic machines generally use a two-component developer mix comprising a toner powder and a magnetizable carrier material. During the use of the apparatus, toner powder has to be replenished in a quantity necessary to compensate for the consumption of toner powder used for the development of images. Various automatic toner replenishment systems are known wherein a signal representative of the detected concentration of toner powder in the developer mix is compared with a reference signal corresponding to a predetermined reference toner concentration. When the detected concentration is lower than the reference concentration, replenishment occurs.
The reference signal is fixed during manufacture, but re-setting in the field is often necessary when the developer mix is changed. U.S. Pat. No. 4,708,458, which issued to Ueda et al on Nov. 24, 1987, discloses a system which, when activated at the time of replacement of the used developer mix with new mix, resets the reference signal. Thereafter, the signal representative of the detected concentration is compared to the reset reference signal.
In some copiers and printers, entire development stations are replaceable when its original supply of toner is exhausted. Commonly assigned U.S. patent application Ser. No. 116,200, now U.S. Pat. No. 4,797,704 filed in the names of L. A. Hill et al on Nov. 3, 1987, discloses a disposable (and therefore replaceable) development station which is completely sealed after being loaded with developer and toner materials. Accordingly, the useful life of the station is determined by the single supply of toner power therein.
While the system of previously-mentioned U.S. Pat. No. 4,708,458 for resetting the reference signal at the time of change of the developer mix would be useful with replaceable development stations such as taught by application Ser. No. 116,200, now U.S. Pat. No. 4,797,709 there would exist a risk that an operator would forget to activate the resetting system. This would result in a false reference signal set to the previous development station characteristics.